A public-use single-row eccentric thrust bearing assembly heretofore known in the art includes a pair of races, and rolling elements interposed between these races. This bearing assembly has a structure wherein a plurality of rolling elements such as balls are interposed between the two plate-like races in opposing relation. Thus, the two races are allowed to move in a manner to decenter as radially shifted from each other and are also allowed to pivotally move relative to each other.
A public-use double-row eccentric thrust bearing assembly heretofore known in the art includes: a single inner race; two outer races opposing either side of the inner race; and two rows of rolling elements interposed between these races. This double-row eccentric thrust bearing assembly includes the two outer races, whereas the two rows of rolling elements bear axial loads in mutually opposite directions, respectively, whereby the bearing assembly is able to bear the axial loads in the opposite directions.
Some of the public-use eccentric thrust bearing assemblies permit the inner race and the outer races to be freely rotate relative to each other.
In such single-row and double-row eccentric thrust bearing assemblies in public use, the balls as the rolling elements are randomly disposed in space between the races, or arranged in a full-type ball bearing fashion.
The conventional eccentric thrust bearing assemblies have some problems.
A first problem pertains to the conventional single-row eccentric thrust bearing assembly. The conventional single-row eccentric thrust bearing assembly is able to bear the axial load in one direction, or the load acting in the direction to compress the rolling elements, but is unable to bear the axial loads in the opposite directions. That is, the bearing assembly is unable to bear the axial load acting in a direction to draw the two opposite races apart from each other. In order to bear the axial loads in the opposite directions, the bearing assembly must be constructed as the double-row thrust bearing wherein the rolling elements are arranged in two rows (double-row type). In the case of the double-row bearing assembly, however, the problem (first problem) arises that a bearing width (axial width of the bearing assembly) is increased.
A second problem pertains to the conventional double-row thrust bearing assembly which includes a large race portion. In cases, therefore, it is extremely difficult to machine the race portion. For instance, it is extremely difficult to ensure the flatness of a raceway surface. Hence, it is not easy to fabricate a larger bearing assembly. Furthermore, since the race portion formed from an iron-base metal such as a bearing steel is large in size, the bearing assembly is increased in weight. This also leads to difficulty in reducing the weight of the bearing assembly.
A third problem is an excessive energy loss because the conventional double-row eccentric thrust bearing assembly suffers great resistance during operation. In a case where the rolling elements are randomly disposed or arranged in a full-type ball bearing fashion, as described above, the rolling elements contact each other and rub against each other to produce friction therebetween. As a countermeasure against this problem, it may be contemplated to employ a cage for maintaining a relative positional relation among the rolling elements. In this case, however, the friction results from sliding contact between the cage and the race.
A fourth problem pertains to a fact that no investigation has ever been made to define a proper gap between inside and outside members with respect to a decenterable range of the bearing assembly, the inside and outside members provided for decentering movement. Hence, the gap between the inside and outside members and the size of the race or the like are greater than necessary, so that the bearing assembly has an unduly great size. This results in the increased weight and cost of the bearing assembly.
In view of the foregoing problems, the invention has been accomplished, providing an eccentric thrust bearing assembly capable of bearing the axial loads in the opposite directions.
A first object of the invention is to solve the first problem and to provide an eccentric thrust bearing assembly which features a smaller bearing width than that of the double-row structure, and which is capable of bearing the axial loads in the opposite directions.
A second object of the invention is to solve the second problem and to provide a double-row eccentric thrust bearing assembly which facilitates the upsizing and weight reduction of the bearing assembly by reducing the size of the race portion.
A third object of the invention is to solve the third problem and to provide a double-row eccentric thrust bearing assembly which permits relative movement of a constant distance and suffers an extremely low energy loss associated with the relative movement.
A fourth object of the invention is to solve the fourth problem and to provide a double-row eccentric thrust bearing assembly permitting free relative rotation, which defines a more optimum gap between the individual members with respect to the decenterable range of the bearing assembly thereby achieving the downsizing and weight reduction of the bearing assembly.